Scintillating detectors for quality assurance of a therapy photon beam

ABSTRACT

The present disclosure relates to scintillating detector systems for radiation therapy beams. In one implementation, a detector system for evaluating radiation delivered by a radiation beam output from a beam generator may include a phantom enclosing an internal volume and having an outer surface, extending around the internal volume, for exposure to radiation, and an inner surface coated, at least in part, with a scintillating material and facing the internal volume. The system may further include a camera external to the enclosed volume and configured to view at least a portion of the inner surface, through an opening of the hollow phantom, when radiated by the radiation beam. The system may further include at least one processor configured to receive images from the camera and calculate, based on the received images, a spatial dose distribution produced by the radiation delivered by the radiation beam to the hollow phantom.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is the National Stage under 35 U.S.C. § 371 ofInternational Application No. PCT/EP2019/069709, filed Jul. 22, 2019,which claims the benefit of priority of U.S. Provisional PatentApplication No. 62/701,890, filed Jul. 23, 2018, which are herebyincorporated by reference in their entireties.

TECHNICAL FIELD

This disclosure relates generally to the field of radiotherapy phantomswith integrated detectors. More specifically, and without limitation,this disclosure relates to scintillating detectors for a photon beam.

BACKGROUND

In radiation therapy, a phantom is often used to determinecharacteristics of a photon beam to be used for treatment. For example,the phantom may be used to verify if the beam sequence applied to thepatient fulfills the clinical requirements or to adjust the beam priorto treating a patient or subject.

However, most of such phantoms use a plurality of single detectors tocharacterize the photon beam. Accordingly, phantoms may be costly toproduce if a high number of detectors is used. In addition, mostdetector or sensor configurations fail to achieve spatial resolutionbetter than 5 mm. Moreover, some treatments, like stereotactictreatments, may require spatial resolution of about 1 mm, which mostexisting phantoms cannot provide.

SUMMARY

Systems and methods of the present disclosure may include scintillatingdetectors having greater spatial resolution than extant detectors. Forexample, by using light emission from scintillating material,embodiments of the present disclosure may allow for more accuratequality assurance of a particular beam. Furthermore, some embodimentsmay use one or more additional detectors placed in the isocenter orother special points of interest. Moreover, mirrors or totallyreflecting surfaces might be used to increase the field of view for thescintillation light or to further improve the spatial resolutionprovided by the scintillating detector and to embed the scintillatingzone in a material selected for dosimetric properties.

According to an exemplary embodiment of the present disclosure, ascintillating detector for evaluating radiation delivered by a radiationbeam may comprise a phantom enclosing an internal volume and having: anouter surface, extending around the internal volume, for exposure toradiation, and an inner surface coated, at least in part, with ascintillating material and facing the internal volume; a camera externalto the enclosed volume and configured to view at least a portion of theinner surface, through an opening of the phantom, when radiated by theradiation beam; and at least one processor configured to receive imagesfrom the camera and calculate, based on the received images, a spatialdose distribution produced by the radiation delivered by the radiationbeam to the phantom.

In some embodiments, the phantom may be translationally symmetric alongat least one axis. For example, the phantom may be cylindrical.

Additionally or alternatively, the phantom may be not rotationallysymmetric about the at least one axis. For example, the phantom may havean elliptical cross section.

In any of the embodiments above, the phantom is made of plastic.Additionally or alternatively, the volume may be filled with a lighttransparent material (e.g., in order to include radiation backscattereffects). Additionally with or alternatively to a solid transparentfilling, water or another transparent liquid may fill the volume of thephantom.

In any of the embodiments above, the system may further comprise one ormore point sensors placed along an axis of the volume (or in otherpoints of interest). The point sensor may be held in place by a holderconnected to a wall of the hollow phantom. In some embodiments, thepoint sensor may also be made out of scintillating material and may beplaced in a field of view of the camera.

In any of the embodiments above, the device may further comprise one ormore reflective surfaces placed between the scintillating material andan axis of the phantom.

According to another exemplary embodiment of the present disclosure, amethod of determining a dose distribution created by a radiation beammay comprise controlling a radiation generator to generate the radiationbeam, controlling a delivery system to deliver the radiation beam to aphantom having a scintillating material for a particular time, receivingimages of the phantom receiving the radiation beam converting thereceived images created by scintillation light to doses, and integratingthe doses over time to obtain the resulting dose distribution.

In some embodiments, the method may further comprise comparing the dosedistribution to a predicted dose distribution; and applying one or morecorrections to the measured images. For example, the one or morecorrections may include at least one of a correction for the incidentenergy, a correction for the energy distribution, a correction forgeometric distortion, and a correction for the angle of incidence. Forexample, the one or more corrections may be applied to the measuredimages during the conversion of the images to a dose distribution, inorder to compensate for effects related to the sensor response limitingits dosimetric performances.

Another possibility is to apply the correction to the predicted dosedistribution, and to convert the corrected predicted dose distributionto a predicted measured signal (e.g., predicted images). In this case,the measured images may be directly compared to the predicted images.

According to another exemplary embodiment of the present disclosure, amethod of determining positional dose distributions of a radiation beammay comprise controlling a scanner (e.g., a Computed Tomography (CT) orMagnetic Resonance Imaging (MRI) scanner) to perform a scan of a phantomhaving a scintillating material; controlling a radiation generator togenerate the radiation beam; controlling a delivery system to deliverthe radiation beam to the phantom for a particular time; receivingimages of the phantom receiving the radiation beam; converting thereceived images to doses based on signals output by the scintillatingmaterial; integrating the doses over time obtain to the dosedistribution; and determining positional dose distributions based on thedose distribution and the scan of the phantom.

In addition to or alternative to using the scan to map the dosedistributions to positions, the scan may be used, in combination with aradiation treatment plan, to predict positional dose distributions overthe phantom. Accordingly, the predicted positional dose distributionsmay be compared with the determined positional dose distributions, asexplained further below.

In some embodiments, the method may further comprise comparing thepositional dose distributions to predicted positional dosedistributions; and applying one or more corrections to the measuredimages. As explained above, the one or more corrections may include atleast one of a correction for the incident energy, a correction for theenergy distribution, a correction for geometric distortion, and acorrection for the angle of incidence. For example, the one or morecorrections may be applied to the measured images during the conversionof the images to a dose distribution, in order to compensate for effectsrelated to the sensor response limiting its dosimetric performances.

As explained above, the possibility is to apply the correction to thepredicted dose distribution, and to convert the corrected predicted dosedistribution to a predicted measured signal (e.g., predicted images). Inthis case, the measured images may be directly compared to the predictedimages.

Additional objects and advantages of the present disclosure will be setforth in part in the following detailed description, and in part will beobvious from the description, or may be learned by practice of thepresent disclosure. The objects and advantages of the present disclosurewill be realized and attained by means of the elements and combinationsparticularly pointed out in the appended claims.

It is to be understood that the foregoing general description and thefollowing detailed description are exemplary and explanatory only, andare not restrictive of the disclosed embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which comprise a part of this specification,illustrate several embodiments and, together with the description, serveto explain the disclosed principles. In the drawings:

FIG. 1A is a schematic representation of a scintillating detector,according to an exemplary embodiment of the present disclosure.

FIG. 1B is a schematic representation of another scintillating detector,according to an exemplary embodiment of the present disclosure.

FIG. 2A is a schematic representation of a scintillating detector withan isocenter sensor, according to an exemplary embodiment of the presentdisclosure.

FIG. 2B is a schematic representation of another scintillating detectorwith an isocenter sensor, according to an exemplary embodiment of thepresent disclosure.

FIG. 3A is a schematic representation of a scintillating detector withreflective surfaces, according to an exemplary embodiment of the presentdisclosure.

FIG. 3B is a schematic representation of a scintillating detector withreflective surfaces and an isocenter sensor, according to an exemplaryembodiment of the present disclosure.

FIG. 3C is a schematic representation of an anti-scattering grid for usein a scintillating detector, according to an exemplary embodiment of thepresent disclosure.

FIG. 3D is a schematic representation of a pixel mask for use in ascintillating detector, according to an exemplary embodiment of thepresent disclosure.

FIG. 3E is a schematic representation of a distorted image of the pixelmask of FIG. 3D.

FIG. 3F is a schematic representation of a corrected image of the pixelmask of FIG. 3D.

FIG. 4 is a schematic illustration of entry and exit points of aradiation beam into a scintillating detector, according to an exemplaryembodiment of the present disclosure.

FIG. 5A is a schematic representation of a trunk-like scintillatingdetector, according to an exemplary embodiment of the presentdisclosure.

FIG. 5B is a schematic representation of a trunk-like scintillatingdetector with an end cap, according to an exemplary embodiment of thepresent disclosure.

FIG. 5C is a schematic representation of a scintillating detector withcontinuously decreasing cross-sectional area, according to an exemplaryembodiment of the present disclosure.

FIG. 6 is a flowchart of a method for determining a dose distribution ofa radiation beam, according to an exemplary embodiment of the presentdisclosure.

FIG. 7 is a schematic representation of coordinate systems for ascintillating detector and a camera, according to an exemplaryembodiment of the present disclosure.

DETAILED DESCRIPTION

The disclosed embodiments relate to scintillating detectors and methodsof use of the same. For example, embodiments of the present disclosuremay be used to perform quality assurance on a radiation beam.

According to an embodiment of the present disclosure, a detector systemfor evaluating radiation delivered by a radiation beam output from abeam generator may comprise a hollow phantom enclosing a volume orcavity and having an outer surface for exposure to radiation and aninner surface coated, at least in part, with a scintillating material.The hollow phantom may comprise any shape. For example, the hollowphantom may have translational symmetry along at least one axis.Accordingly, the hollow phantom may be cylindrical. Additionally oralternatively, the hollow phantom may not be rotationally symmetricalabout the at least one axis. Accordingly, the hollow phantom may have anelliptical, rather than circular, base.

In any of the embodiments above, the hollow phantom may further comprisean end cap. For example, the end cap may comprise a semi-spherical,semi-ellipsoid, or the like. Additionally or alternatively, the hollowphantom may have a cross-sectional area that decreases along at leastone axis. For example, the hollow phantom may have a circular orelliptical cross-section with a radius or an axis that decreases alongan axis of the hollow phantom.

The inner surface may be coated, at least in part, with a scintillatingmaterial. For example, the scintillating material may comprise aninorganic or organic scintillator, such as anthracene, stilbene,naphthalene, a scintillating solution, or the like. Additionally oralternatively, the scintillating material may comprise a plasticscintillator having a fluor suspended in or bonded to a base comprisinga polymeric matrix. Accordingly, when the radiation passes through thephantom, the scintillating material will transmit a signal, i.e.,illuminate, due to the radiation. The scintillating surface may beuniformly coated or sub-divided into one or more smaller scintillatingspots. Additionally with or alternatively to sub-division intoscintillating spots, a pixel mask with narrow openings may provide agranular light emission from the phantom.

Although described as “coated,” the inner surface may comprisescintillating material in other ways. For example, a foil ofscintillating material may be placed or otherwise attached (e.g., viaadhesive or the like) to the phantom such that the foil comprises theinner surface. In such embodiments, the foil or other scintillatingmaterial placed on or otherwise attached to the phantom may be uniformor sub-divided into one or more smaller scintillating spots.

The scintillating detector may further comprise a camera (e.g.,comprising a lens system and converter to electrical signal, like a CCDor CMOS sensor) external to the enclosed volume and configured to viewat least a portion of the inner surface through an opening of the hollowphantom. Accordingly, the camera may capture images of the illuminationof the scintillating material caused by the radiation. In someembodiments, an accelerator used to generate the radiation may generateshort pulses, e.g., having a period between 1 ms and 10 ms. Accordingly,the images may be synchronized with the pulses in order to increase thesignal-to-noise ratio. The camera may capture such images sequentiallyduring a particular treatment time. The camera may further includeoptical filters to limit the sensitivity to a wavelength band or tocut-off the lower or higher end of the wavelength spectrum. The camera(optionally with its lens) may be embedded in air, water or anothertransparent gas or liquid.

The scintillating detector may further comprise at least one processorconfigured to receive images from the camera and calculate arepresentation of a dose of the radiation based on the received images.For example, the at least one processor may use one or more propertiesof the illumination radiation such as wavelength, brightness, shape, orthe like, to determine properties of the beam, such as amplitude,wavelength, energy spread, or the like. These properties may be mappedonto known locations of the scintillating material to determinepositional dose distributions of the radiation. For example, the knownlocations may be derived from a scan of the hollow phantom, e.g., acomputed tomography (CT) scan.

The at least one processor may adjust brightness of one or more firstpixels corresponding with scintillating portions of the received imagesbased on brightness of one or more second pixels corresponding withnon-scintillating portions of the received images. For example, asexplained above, the inner surface may be sub-divided into one or moresmaller scintillating spots. Accordingly, the one or more scintillatingspots may result in scintillating portions of the images captured by thecamera while the non-scintillating spots (also called “dark” spots) mayresult in the non-scintillating portions (also called “dark” portions)of the images captured by the camera. Similarly, in embodiments wherethe foil or other scintillating material placed on or otherwise attachedto the phantom is sub-divided into one or more smaller scintillatingspots, the one or more scintillating spots may result in scintillatingportions of the images captured by the camera while thenon-scintillating spots (also called “dark” spots) may result in thenon-scintillating portions (also called “dark” portions) of the imagescaptured by the camera.

Reference will now be made in detail to exemplary embodiments andaspects of the present disclosure, examples of which are illustrated inthe accompanying drawings.

FIG. 1A is a schematic representation of a scintillating detector 100.Detector 100 may comprise a hollow phantom 101. As described above,hollow phantom 101 may be cylindrical. Alternatively, hollow phantom 101may have an elliptical cross-section and/or may have a cross-sectionalarea that decreases along at least one axis. Detector 100 may furthercomprise a camera 103. Camera 103 is configured to view the innersurface of phantom 101 through an opening facing camera 103. The openingmay comprise an uncovered surface of phantom 101 or may comprise atransparent material (whether solid or liquid, as discussed above)through which camera 103 may obtain images of the inner surface ofphantom 101.

As further depicted in FIG. 1A, detector 100 may comprise a computer 105or other processing device (such as a central processing unit (CPU),graphics processing unit (GPU), field-programmable gate array (FPGA),application specific integrated circuit (ASIC), or the like) to performanalysis on images captured by camera 103. Although depicted as separatein FIG. 1A, computer 105 may be integrated with camera 103, e.g., byusing one or more integrated circuits (ICs) of camera 103 to perform theanalysis.

As further depicted in FIG. 1, phantom 101 may receive a radiation beam109 generated by radiation generator 107. Generator 107 may comprise alinear accelerator (LINAC) system or other system that generatesradiation beam 109. In addition, a delivery system may direct radiationbeam 109 to phantom 101. For example, as depicted in FIG. 1, thedelivery system may comprise a plurality of magnets, such as bendingmagnets 111 a, 111 b, 111 c, and 111 d and/or focusing magnets, such asfocusing magnet 111 e. The magnets may comprise dipole magnets,quadrupole magnets, or any combination thereof. As known in the art, thelinear accelerator may generate a radiation beam 109 for delivery to apatient for treatment or, as discussed more below, to phantom 101. Thedisclosed embodiments may be used with any known type of linearaccelerator used to deliver a radiation beam for radiation therapypurposes, such as linear accelerators having a rotatable gantry, havinga kilovoltage (KV) imaging system, or a megavoltage (MV) imaging system.

Computer 105 may perform image analysis functions on images from camera103 in order to calculate a representation of a dose of a radiationdelivered to phantom 101. The representations may be spatial, temporal,or integrated, at least in part, over space and/or time. Computer 105may further compare the calculated dose representation to a predicteddose representation. Deviations from the predicted dose representationmay be used to adjust the accelerator or radiation source used fortreatment, and/or to adjust one or more lenses or other focusinginstruments used to direct the radiation to phantom 101. Alternatively,computer 105 may use a predicted dose to derive an expected measurement(e.g., an expected light intensity) from camera 103. Computer 105 maythen compare the expected measurement to the actual measurement, and tothen perform adjustments accordingly, as explained above. Computer 105may, for example, be part of a conventional treatment planning systemused, as known in the art, to generate a radiation treatment plan andcontrol a linear accelerator system in order to deliver a radiation beamfor treating a patient in accordance with the generated radiationtreatment plan.

FIG. 1B is a schematic representation of another scintillating detector100′. Detector 100′ may comprise a hollow phantom 101 as depicted inFIG. 1A. As depicted in FIG. 1B, phantom 101 may comprise an outersurface 101 a for receiving radiation. For example, outer surface 101 amay comprise a plastic shell. As further depicted in FIG. 1B, phantom101 may comprise an inner surface 101 b made of a scintillatingmaterial. Although not depicted in FIG. 1A, outer surface 101 a andinner surface 101 b are also present in phantom 101 of FIG. 1A.

As used herein, the term “surface” refers to a three-dimensional surfacehaving depth (e.g., a layered surface) and not merely to thetwo-dimensional surface area of an object. For example, the outersurface 101 a may comprise a plurality of plastic layers bonded togetherto form the plastic shell that encloses a cavity or space. In anotherexample, inner surface 101 b may comprise a supporting plastic as wellas the scintillating material (or a plurality of scintillating layers)bonded together. As explained above, the scintillating material may bearranged as a uniform layer or may be sub-divided into pixels or othersmaller regions optically isolated from each other. Surface 101 a isreferred to as an “outer” surface because it is provided on top of an“inner” surface (surface 101 b). In other words, the terms “inner” and“outer” are used to relate the surfaces relative to each other ratherthan relative to any absolute measure.

As further depicted in FIG. 1B, camera 103′ may be integrally formedwith phantom 101. For example, one or more supports may connect camera103′ to phantom 101. Moreover, camera 103′ may be focused by one or morelenses, e.g., lens 105′, installed between camera 103′ and phantom 101.Although not depicted in FIG. 1B, computer 105 of FIG. 1A may also beincluded in detector 100′.

FIG. 2A is a schematic representation of a scintillating detector 200.Detector 200 may comprise a hollow phantom 201. Hollow phantom 201 maybe similar to hollow phantom 101 of FIGS. 1A and 1B. In addition, camera203 and computer 205 may be similar to camera 103 of FIG. 1A (or camera103′ of FIG. 1B) and computer 105 of FIGS. 1A and 1B, respectively.

As depicted in FIG. 2A, phantom 201 may further comprise an isocentersensor 203. For example, isocenter sensor 203 may comprise any type ofsensor, such as an ionization chamber, luminescent sensor, or the like.Alternatively, the isocenter sensor 203 may comprise a small body havingan internal cavity visible to camera 203 and coated with the samescintillating material used on the inner surface of phantom 201.Accordingly, isocenter sensor 203 may produce measurements dependent onthe relationship between the thickness of the scintillating material andthe radiation strength rather than on the details of the sensor surface.

As further depicted in FIG. 2A, isocenter sensor 203 may be centered onone or more axes of phantom 201. For example, isocenter sensor 203 iscentered on axis 205 b, around which phantom 201 has translationalsymmetry. In addition, isocenter sensor 203 is centered on axis 205 b,which may represent an axis of the radiation.

FIG. 2B is a schematic representation of another scintillating detector200′. Detector 200′ may comprise a hollow phantom 201 and a camera 203,as depicted in FIG. 2A. Although not depicted in FIG. 2B, computer 205of FIG. 2A may also be included in detector 200′.

As depicted in FIG. 2B, phantom 201 may comprise an outer surface 201 afor receiving radiation. For example, outer surface 201 a may comprise aplastic shell. As further depicted in FIG. 2B, phantom 201 may comprisean inner surface 201 b made of a scintillating material. Although notdepicted in FIG. 2A, outer surface 201 a and inner surface 201 b arealso present in phantom 201 of FIG. 2A.

As further depicted in FIG. 2B, phantom 201 may further comprise anisocenter sensor 203 as depicted in FIG. 2A. Isocenter sensor 203 may beheld in place using holder 207. Holder 207 may connect to any portion ofinner surface 201 b. To avoid interfering with camera 203, holder 207may connect to a portion of inner surface 201 b further from camera 203than isocenter sensor 203. Although not depicted in FIG. 2A, holder 207may also present in phantom 201 of FIG. 2A.

FIG. 3A is a schematic representation of a hollow phantom 300, which maybe used in a scintillating detector of the present disclosure. Hollowphantom 300 may be similar to hollow phantom 101 of FIGS. 1A and 1B.

As depicted in FIG. 3A, phantom 300 may enclose a volume 301 and maycomprise an outer surface 301 a for receiving radiation. For example,outer surface 301 a may comprise a plastic shell. As further depicted inFIG. 3A, phantom 300 may comprise an inner surface 301 b made of ascintillating material. Phantom 300 may also include one or more opticalanti-scattering grids 301 c to prevent reflectors 303 a and 303 b fromscattering light from a direction non-normal to the scintillator shellof phantom 300.

As further depicted in FIG. 3A, phantom 300 may include one or morereflective surfaces, e.g., reflectors 303 a and 303 b. Reflectors 303 aand 303 b may reflect any signal generated by inner surface 301 b towardthe camera (not shown). This may allow for the entire image of thecamera to include information about the radiation rather than only aportion of the image. In such an embodiment, the computer (not shown)may have to perform post-processing on the received images to correctfor distortions in the image caused by reflectors 303 a and 303 b, e.g.,based on known locations and shapes of reflectors 303 a and 303 b.

FIG. 3B is a schematic representation of a phantom 300′, which may beused in a scintillating detector of the present disclosure. Phantom 300′may enclose a volume 301 as depicted in FIG. 3A.

Similar to FIG. 3A, phantom 300′ may comprise an outer surface 301 a forreceiving radiation. For example, outer surface 301 a may comprise aplastic shell. In addition, phantom 300′ may comprise an inner surface301 b made of a scintillating material. Phantom 300′ may also includeone or more anti-scattering grids 301 c to prevent reflectors 303 a and303 b from scattering light from a direction non-normal to thescintillator shell of phantom 300′.

Similar to FIG. 3A, phantom 300′ may include one or more reflectivesurfaces, e.g., reflectors 303 a and 303 b. Reflectors 303 a and 303 bmay reflect any signal generated by inner surface 301 b toward thecamera (not shown). As further depicted in FIG. 3B, phantom 300′ mayinclude an isocenter sensor 305 similar to sensor 203 depicted in FIGS.2A and 2B. In addition, isocenter sensor 305 may be held in place byholder 307 similar to holder 207 depicted in FIG. 2A.

In any of the embodiments depicted in FIG. 1A, 1B, 2A, 2B, 3A, or 3B,the hollow phantom may further include an anti-glare filter (oranti-scatter grid 301 c, as described with respect to FIG. 3A) on theinner surface of the scintillator grid. This filter (or grid) may ensurethat light rays leave the scintillator only in the normal direction orthe direction which leads to a direct image on the camera sensor. Thismay reduce glare present in the received images, resulting in bothimproved spatial resolution and reducing post-processing needs.

In any of the embodiments depicted in FIG. 1A, 1B, 2A, 2B, 3A, or 3B,the hollow phantom may be filled with a solid or liquid that istransparent to the signal emitted by the scintillating material.Accordingly, in FIGS. 3A and 3B, reflectors 303 a and 303 b may comprisean interface between the solid or liquid filling the phantom and airsurrounding isocenter sensor 305 or at least a middle portion of thephantom. For example, reflectors 303 a and 303 b may comprise a plasticacting as an interface between the solid or liquid filling the phantomand the air.

Moreover, in such embodiments, Cherenkov radiation may be emitted in thebackscatter medium (that is, the solid or liquid filling the phantom).This may be, for example, concentrated in the blue spectral range.Accordingly, in such embodiments, the scintillator material may beselected to emit at a different wavelength (e.g., red) and/or using afilter (e.g., an edge or a band-pass filter) in front of the camera (notshown) in order to discriminate the signal from the Cherenkov radiation.Such a discrimination might be performed as well by using a processingof information from color channels of the camera. As explained above,the scintillator may be replaced by a thick (e.g., 2 cm layer oftranslucent material with a high refractive index (e.g., 1.5) or water,using Cerenkov radiation instead of scintillation light for theradiation detection.

FIG. 3C is a schematic representation of an anti-scattering grid 310 foruse in a scintillating detector. For example, anti-scattering grid 310may be used as anti-scattering grid 301 c of FIGS. 3A and 3B. Asdepicted in FIG. 3C, grid 310 may comprise alternating strips 311 a and311 b of a radiation absorbing substance (e.g., lead) and a radiolucentsubstance (e.g., plastic, carbon fibre, aluminium, paper, or the like).

FIG. 3D is a schematic representation of a pixel mask 320 for use in ascintillating detector. For example, pixel mask 320 may be used inaddition to or in lieu of anti-scattering grid 301 c of FIGS. 3A and 3B.Pixel mask 320 may be formed of a bulk material or may comprise a thinnon-transparent sheet with one or more openings, e.g., opening 321 a and321 b. Although depicted as elliptical, the openings may be anygeometric shape, such as square, circular, hexagonal, or the like.Although depicted as of uniform shape, the openings may comprisedifferent shapes. The mask may comprise a material having similarreflective properties as the scintillating layer, such that the lightreflected at non-transparent parts of the mask may be representative forthe reflection of scattered light in open parts of the mask.Accordingly, the light reflected at one or more of the non-transparentparts may be used for optical backscatter correction in post-processing.The mask, whether arranged as a regular pattern or in any othergeometric configuration (or an arrangement of individual scintillatingpixels, whether arranged as a regular pattern or in any other geometricconfiguration) may be used to determine the position of one or moreelements of the scintillating surface on a resulting camera image. Thus,the mask or other arrangement of scintillating pixels may be used forthe localization of points on the surface of the phantom and/or fordistortion correction of a calculated dosimetric image.

FIG. 3E is a schematic representation of a distorted image 330 of thepixel mask 320 of FIG. 3D. For example, as shown in FIG. 3E acharge-coupled device (CCD) camera may distort the pattern in which theopenings (such as openings 331 a and 331 b) are arranged. Accordingly,at least one processor (e.g., of a computer processing images from thecamera) may correct distorted image 330 to corrected image 349 (shown inFIG. 3F) based on the known arrangement of the openings in pixel mask320.

FIG. 4 is an example of a radiation beam 403 passing through a hollowphantom. Similar to FIGS. 1B, 2B, 3A, and 3B, the hollow phantom maycomprise an outer surface 401 a for receiving radiation from beam 403and an inner surface 401 b made of a scintillating material. Althoughnot depicted in FIG. 4, the hollow phantom may further include one ormore reflectors, an isocenter sensor, and/or an anti-scattering grid oranti-glare filter, as described above.

As depicted in FIG. 4, beam 403 intersects inner surface 401 b atlocations 405 a and 405 b. Accordingly, in an image of the hollowphantom of FIG. 4, the signal from inner surface 401 b will appear nearlocations 405 a and 405 b. In embodiments having reflectors, the signalwill also appear in locations where it is reflected. Accordingly, theprofile of beam 403 may be determined using captured images, optionallymapped to information about the shape, density, and locations of innersurface 401 b and, in embodiments with reflectors, of the reflectors.

FIG. 5A is an example of a scintillating detector 500 having asymmetrical phantom 501. As depicted in FIG. 5A, phantom 501 hastranslational symmetry along axis 505 b. Accordingly, axis 505 a mayrepresent a possible axis of entry for a beam.

FIG. 5B is an example of a scintillating detector 500′ having a phantom501′ with an end cap. As depicted in FIG. 5B, phantom 501′ is notsymmetrical along axis 505 b because of the end cap, which may besemi-spherical, semi-ellipsoid, or the like. Accordingly, axis 505 a′may represent a possible axis of entry for a beam to phantom 501′, anaxis of entry not usable with phantom 501 of FIG. 5A.

FIG. 5C is an example of a scintillating detector 500″ having a phantom501″. As depicted in FIG. 5C, phantom 501″ is not symmetrical along axis505 b because it has a decreasing cross-sectional area along axis 505 b.The decrease may be continuous, as depicted in FIG. 5C, or may bepartially discontinuous, e.g., having one or more lengths of constant orincreasing cross-sectional area along axis 505 b. Accordingly, axis 505a″ may represent a possible axis of entry for a beam to phantom 501″, anaxis of entry not usable with phantom 501 of FIG. 5A or phantom 501′ ofFIG. 5B.

In all of FIGS. 5A, 5B, and 5C, camera 503 is configured to view aninner surface of the phantom. Although not depicted, computer 105 ofFIG. 1A and/or computer 205 of FIG. 2A may also be included in any ofdetectors 500, 500′, and 500″.

FIG. 6 depicts method 600 for determining a dose distribution of aradiation beam. Method 600 may be performed by, for example, computer105 of FIG. 1A, computer 205 of FIG. 2A, or any other general-purpose orspecial-purpose computing device.

At step 601, the processing device 105, 205 may control a beam generatorto generate the radiation beam. For example, the processing device maycontrol a linear accelerator (LINAC) system or other system thatgenerates a radiation beam and directs it to a particular location.

At step 603, the processing device 105, 205 may control a deliverysystem to deliver the radiation beam to a phantom (e.g., phantom 101,phantom 201, phantom 301, phantom 501, phantom 501′, or phantom 501″)having a scintillating material for a particular time. For example, theprocessing device 105, 205 may control the linear accelerator, or afocal system that receives the beam generated by the linear accelerator,to direct the generated beam to the phantom. The phantom may compriseany phantom described above (e.g., phantom 101, phantom 201, phantom301, phantom 501, phantom 501′, or phantom 501″) or otherwise consistentwith the present disclosure.

At step 605, the processing device 105, 205 may receive images of thephantom receiving the radiation beam. For example, the processing device105, 205 may receive the images from a camera 103 viewing thescintillating material of the phantom. Accordingly, the images mayinclude one or more bright spots caused by a signal released from thescintillating material caused by the radiation beam. For example, thebright spots may represent the entry and exit points of the beam intothe phantom.

The received images may comprise camera frames captured during the timeof the radiation. The received images may also include frames capturedbefore the radiation and/or after the radiation. In embodiments wherethe frames are monochromatic, the processing device 105, 205 may extractraw data from the received images, the raw data comprising intensity asa function of location (e.g., x and y components of pixels of theimages) and time (e.g., depending on the frame from which the data isextracted). The processing device 105, 205 may transform the timemeasured in frames into absolute time (such as Coordinated UniversalTime (UTC)) based on a reference absolute time, e.g., an absolute timefor at least one frame, and a frame rate of the camera.

In embodiments where the frames are in color, the processing device 105,205 may extract raw data from the images, the raw data comprising atleast three sets of images (e.g., corresponding to red, blue and greenchannels), each with intensity as a function of location (e.g., x and ycomponents of pixels of the images) and time (e.g., depending on theframe from which the data is extracted). In other color encodingschemes, a greater number of channels may be used. For example, a CYGMscheme may use four channels (cyan, yellow, green, magenta), a RGBEscheme may use four channels (red, green, blue, emerald), and a CMYWscheme may use four channels (cyan, magenta, yellow, and white). Theprocessing device 105, 205 may combine the sets of images to generate agrayscale data set similar to the monochromatic data set describedabove.

At step 607, the processing device 105, 205 may convert the receivedimages to representations of doses based on signals output by thescintillating material. For example, the processing device 105, 205 maycalculate the representations of doses of the beam corresponding to theimages based on brightness, wavelength, and/or other properties of thebright spots and known relations between the bright spot properties andthe beam (e.g., which particles of the beam produce which wavelengths,which amplitudes of the beam produce which brightnesses, or the like).

The processing device 105, 205 may use three reference frames whenperforming the conversion, as depicted in FIG. 7. As depicted in FIG. 7,(x,y) may indicate the two-dimensional frame of pixels of the cameraand, accordingly, of the received images. As also depicted in FIG. 7,(x′,y′,z′) may indicate the three-dimensional frame onto which, forexample, the received images may be projected. As further shown, (α,β)may indicate the two-dimensional frame of the hollow phantom.

In some embodiments, to convert the images to representations of doses,the processing device 105, 205 may apply one or more correction factorsε_(m) to the intensities of the received images. For example, the one ormore correction factors may account for the sensitivity of thescintillator, sensitivity of the camera 103, and/or dependence ofintensity on parameters, such as beam quality, gain of the measurementchain, or the like. The processing device 105, 205 may multiply,convolve, or otherwise combine the correction factors with theintensities to perform the correction. Fourier transform algorithmsmight be applied to the raw images, processing applied in the momentumspace and re-transformation performed. For example, the doses maycomprise d(x,y,t)=Π_(m)ε_(m)·g(x,y,t), where d(x,y,t) is therepresentation of a dose at location (x,y) and time t, ε_(m) is a set ofm correction factors, and g(x,y,t) is the intensity of the images atlocation (x,y) and time t.

Before or after conversion to representations of doses, the processingdevice 105, 205 may apply pre-processing corrections to the intensitiesor dose representations, respectively. For example, the processing maysubtract the background; perform uniformity correction, or the like. Inone example, pre-processed intensities g(x,y,t)=u(x,y)·[f(x,y,t)−b(x,y)], where f(x,y,t) represents the raw intensities at location(x,y) and time t, b(x,y) represents the background in the images atlocation (x,y), and u(x,y) represents a function imposing uniformity onthe images.

The processing device 105, 205 may project the dose representations fromthe two-dimensional coordinates of the camera 103 to the two-dimensionalphantom surface. Accordingly, the processing device 105, 205 may performtransformation

${{d\left( {x,y,t} \right)}\underset{\omega}{->}{d\left( {\alpha,\beta,t} \right)}},$where ω represents the transformation matrix between d(x,y,t), which isthe dose representation in the two-dimensional coordinate system (x,y)of the camera 103, and d(α,β,t), which is the dose representation in thetwo-dimensional coordinate system (α,β) of the phantom surface.Alternatively, the processing device 105, 205 may project theintensities prior to converting the intensities to dose representations.That is, processing device 105, 205 may perform transformation

${{g\left( {x,y,t} \right)}\underset{\omega}{->}{g\left( {\alpha,\beta,t} \right)}},$presents the transformation matrix between g(x,y,t), which is theintensities in the two-dimensional coordinate system (x,y) of the camera103, and g(α,β,t), which is the intensities in the two-dimensionalcoordinate system (α,β) of the phantom surface.

At step 609, the processing device 105, 205 may integrate the doserepresentations over the particular time to obtain the dosedistribution. For example, the processing device 105, 205 may graph thecalculated dose representations based on times at which thecorresponding images were received from the camera 103. The processingdevice 105, 205 may additionally sum the graphed dose representations toobtain a total dose representation for the particular time.

Steps 607 and 609 may be reversed. Accordingly, the processing device105, 205 may integrate the dose representations prior to transformingthe dose representations to the coordinate system of the phantom (e.g.,d(x,y)=Σ_(t)d(x,y,t), because the dose representations d(x,y,t) must beintegrated discretely over frames rather than continuously over time).Additionally or alternatively, the processing device 105, 205 mayintegrate the intensities prior to converting the intensities to doserepresentations (e.g., g(x,y)=Σ_(t)g(x,y,t)) and/or prior topre-processing the intensities.

Method 600 may further include additional steps. For example, method 600may further include controlling a scanner to perform a scan of thephantom (e.g., phantom 101, phantom 201, phantom 301, phantom 501,phantom 501′, or phantom 501″) having the scintillating material.Accordingly, the processing device 105, 205 may control a scanner toperform (or may receive) a scan, such as a CT or MRI scan, of thephantom and determine a topography of the scintillating material basedon the scan. In such embodiments, the processing device 105, 205 may usethe scan to determine, at least in part, transformation matrix co,discussed above.

Accordingly, method 600 may include determining positional dosedistributions based on the dose distribution and the scan of thephantom. In some embodiments, the processing device 105, 205 may map thegraph of the calculated dose representations and/or the total dose tolocations of the scintillating material on the phantom. Accordingly, theprocessing device 105, 205 may divide the graph of the calculated doserepresentations and/or the total dose representation between an entrypoint of the beam, an exit point of the beam, an isocenter, or any otherlocations to which the doses may be mapped.

In any of the embodiments described above, method 600 may furtherinclude comparing the dose distribution to a predicted dosedistribution. For example, the processing device 105, 205 may transforma predicted dose representation from three-dimensional coordinates totwo-dimensional coordinates on the phantom, e.g.,

${{D\left( {x^{\prime},y^{\prime},z^{\prime},t} \right)}\underset{\omega}{->}{D\left( {\alpha,\beta,t} \right)}},$where D(x′,y′,z′,t) is the predicted dose representation in athree-dimensional coordinate system (x′,y′,z′), and D(α,β,t) is thepredicted dose representation in the two-dimensional coordinate systemon the phantom (α,β). As explained above, the predicted doserepresentation may be based on a radiation treatment plan as well as ascan (e.g., a CT scan, an MRI scan, or the like) of the phantom. Inembodiments where the doses are integrated over time, the processingdevice 105, 205 may integrate the predicted dose representations (orotherwise use a total predicted dose representation) for thetransformation,

${D\left( {x^{\prime},y^{\prime},z^{\prime}} \right)}\underset{\omega}{->}{{D\left( {\alpha,\beta} \right)}.}$

Alternatively, method 600 may compare measured intensities to predictedintensities based on a predicted dose distribution. For example,alternatively to steps 607 and 609, described above, the processingdevice 105, 205 may convert a dose prediction to predicted intensitiesand integrate the predicted intensities to obtain an expected totalmeasurement.

In one implementation of such an alternative embodiments, the processingdevice 105, 205 may project a predicted dose representation (either apredicted dose representation over time or an integrated doserepresentation) from three-dimensional coordinates to two-dimensionalcoordinates on the phantom. Based on properties of the scintillator, theprocessing device 105, 205 may determine a predicted amount of lightemitted based on the dose representation, e.g., D(α,β,t′)→L(α,β,t′),where D(α,β,t′) is the predicted dose representation in thetwo-dimensional coordinate system on the phantom (α,β), and L(α,β,t′) isthe predicted light intensity in the two-dimensional coordinate systemon the phantom (α,β). Any non-ideality of the scintillator may beaccounted for during this determination. For example, the sensitivityand other time-independent properties of the scintillator may beincluded in the determination in addition to time-varying quantities,such as gantry angle, spectrum, field size, dose rate, or the like.

The processing device 105, 205 may then project the predicted light fromthe two-dimensional coordinates of the phantom to the two-dimensionalcoordinates of the camera, e.g., L(α,β,t)→G(x,y,t′), where L(α,β,t′) isthe predicted light intensity in the two-dimensional coordinate systemon the phantom (α,β), and G(x,y,t′) is the predicted light intensity inthe two-dimensional coordinate system of the camera 103 (x,y). Theprocessing device 105, 205 may compare the predicted measurementG(x,y,t′) with the intensities measured by the camera (e.g., g(x,y,t)).The processing device 105, 205 may have pre-processed the intensities,as described above, prior to performing the comparison.

Time-resolved comparisons of G(x,y,t′) and g(x,y,t) may include 3Dmethods, e.g., a 3D gamma analysis. Alternatively, time-resolvedcomparisons of G(x,y,t′) and g(x,y,t) may include 2D methods (such as 2Dgamma) based on interpolation of G(x,y,t′) and/or g(x,y,t) across acommon time axis such that the two functions may be compared directly atany time (e.g., G(x,y,t′) may be interpolated such that time t′ alignswith time t or g(x,y,t) may be interpolated such that time t aligns withtime t′).

Alternatively, as explained above, the processing device 105, 205 mayintegrate the predicted two sets of measurements (e.g., the predictedset G and the measured set g) over time prior to performing thecomparison. For example, G(x,y)=Σ_(t′)G(x,y,t′) and g(x,y)=Σ_(t)g(x,y,t)and then the processing device 105, 205 may compare G(x,y) with g(x,y).The integrated comparison may use reduced processing cycles compared toa time-dependent comparison, described above.

In any of the embodiments described above, method 600 may furtherinclude applying one or more corrections based on the comparison(s). Forexample, the processing device 105, 205 may perform at least one ofenergy correction and angular correction to bring the measured dosedistribution (or the positional dose distributions) closer to thepredicted dose distribution (or predicted positional dosedistributions). The processing device 105, 205 may perform suchcorrections by adjusting the focal system controlled in step 603,described above.

The foregoing description has been presented for purposes ofillustration. It is not exhaustive and is not limited to precise formsor embodiments disclosed. Modifications and adaptations of theembodiments will be apparent from consideration of the specification andpractice of the disclosed embodiments. For example, the describedimplementations include hardware and software, but systems and methodsconsistent with the present disclosure can be implemented with hardwarealone. In addition, while certain components have been described asbeing coupled to one another, such components may be integrated with oneanother or distributed in any suitable fashion.

Moreover, while illustrative embodiments have been described herein, thescope includes any and all embodiments having equivalent elements,modifications, omissions, combinations (e.g., of aspects across variousembodiments), adaptations and/or alterations based on the presentdisclosure. The elements in the claims are to be interpreted broadlybased on the language employed in the claims and not limited to examplesdescribed in the present specification or during the prosecution of theapplication, which examples are to be construed as nonexclusive.Further, the steps of the disclosed methods can be modified in anymanner, including reordering steps and/or inserting or deleting steps.

The features and advantages of the disclosure are apparent from thedetailed specification, and thus, it is intended that the appendedclaims cover all systems and methods falling within the true spirit andscope of the disclosure. As used herein, the indefinite articles “a” and“an” mean “one or more.” Similarly, the use of a plural term does notnecessarily denote a plurality unless it is unambiguous in the givencontext. Words such as “and” or “or” mean “and/or” unless specificallydirected otherwise. Further, since numerous modifications and variationswill readily occur from studying the present disclosure, it is notdesired to limit the disclosure to the exact construction and operationillustrated and described, and accordingly, all suitable modificationsand equivalents may be resorted to, falling within the scope of thedisclosure.

Other embodiments will be apparent from consideration of thespecification and practice of the embodiments disclosed herein. It isintended that the specification and examples be considered as exampleonly, with a true scope and spirit of the disclosed embodiments beingindicated by the following claims.

What is claimed is:
 1. A detector system for evaluating radiationdelivered by a radiation beam output from a beam generator, comprising:a phantom enclosing an internal volume and having: an outer surface,extending around the internal volume, for exposure to radiation, and aninner surface comprising, at least in part, a scintillating material andfacing the internal volume; a camera external to the enclosed volume andconfigured to view at least a portion of the inner surface, through anopening of the hollow phantom, when radiated by the radiation beam; andat least one processor configured to: receive images from the camera;adjust brightness of one or more first pixels corresponding withscintillating portions of the received images based on brightness of oneor more second pixels corresponding with non-scintillating portions ofthe received images; and calculate, based on the adjusted images, aspatial dose distribution produced by the radiation delivered by theradiation beam to the hollow phantom.
 2. The system of claim 1, whereinthe phantom is translationally symmetric along at least one axis.
 3. Thesystem of claim 2, wherein the phantom is cylindrical.
 4. The system ofclaim 2, wherein the phantom is not rotationally symmetric about the atleast one axis.
 5. The system of claim 4, wherein the phantom has anelliptical cross-section.
 6. The system of claim 1, wherein the phantomhas a conical shape.
 7. The system of claim 1, wherein the phantom ismade of plastic.
 8. The system of claim 1, wherein the volume is filledwith a light transparent material.
 9. The system of claim 1, furthercomprising: one or more point sensors placed along an axis of thevolume, wherein the point sensor is held in place by a holder connectedto a wall of the phantom.
 10. The system of claim 9, wherein the pointsensor is made out of the scintillating material and is placed in afield of view of the camera.
 11. The system of claim 1, furthercomprising: one or more reflective surfaces placed between thescintillating material and an axis of the phantom.
 12. A method ofdetermining a dose distribution of a radiation beam, comprising:controlling a radiation generator to generate the radiation beam;controlling a delivery system to deliver the radiation beam to a phantomwith an outer surface, extending around an internal volume of thephantom, for exposure to radiation, and an inner surface comprising, atleast in part, a scintillating material and facing the internal volume;receiving images of the phantom receiving the radiation beam; convertingthe received images to doses based on signals output by thescintillating material; and integrating the doses over time to obtainthe dose distribution.
 13. The method of claim 12, further comprising:applying one or more corrections to the measured images; and comparingthe dose distribution to a predicted dose distribution.
 14. The methodof claim 13, wherein the one or more corrections include at least one ofa correction for the incident energy, a correction for the energydistribution, and a correction for the angle of incidence.
 15. A methodof determining positional dose distributions of a radiation beam,comprising: controlling a scanner to perform a scan of a phantom with anouter surface, extending around an internal volume of the phantom, forexposure to radiation, and an inner surface comprising, at least inpart, a scintillating material and facing the internal volume;controlling a radiation generator to generate the radiation beam;controlling a delivery system to deliver the radiation beam to thephantom; receiving images of the phantom receiving the radiation beam;converting the received images to doses based on signals output by thescintillating material; integrating the doses over time to obtain thedose distribution; and determining positional dose distributions basedon the dose distribution and the scan of the phantom.
 16. The method ofclaim 15, further comprising: applying one or more corrections to themeasured images; and comparing the positional dose distributions topredicted positional dose distributions.
 17. The method of claim 16,wherein the one or more corrections include at least one of a correctionfor the incident energy, a correction for the energy distribution, and acorrection for the angle of incidence.